This invention relates to a system and method for programmable time-varying control, and more particularly to a thermostatic system and method in which the reference temperature can be made to vary hour by hour in a programmed way.
In a control system operating against a significant load, considerable energy can be required to hold the controlled variable at or near a reference value. This happens in a thermostatic system when the uncontrolled value of temperture differs substantially from the desired (reference) temperature. It is a very effective means of reducing energy consumption under such circumstances to identify periods when less control is required and to provide for reducing control during those periods. For example, in the thermostatic control of cooling a home, it is effective to raise the thermostat reference temperature during the early hours of the day before the external temperature reaches its maximum, during sleep periods and for periods when the occupants are going to be away. This can, of course, be done manually. However, in a manual system, it can be overlooked or forgotten and cannot be done as timely or accurately as with an automatic system. Another drawback of a manual system is its inconvenience; for example, if the reference temperature is raised when the occupants leave for some time, when they return, the temperature in the home has equilibrated at an uncomfortably high value and may take considerable time to reach a comfortable range. The present invention provides a system and method wherein the reference temperature is made to vary during the day, assuming a sequence of programmable values. This allows heating or cooling to be automatically initiated so as to reach a new reference temperature by a particular time, for example, when occupants of a home are to return.